1. Field of Invention
The present invention relates generally to transistors and methods thereof, and more particularly to spin transistors and methods thereof.
2. Related Art
Conventional spin transistors may be electronic devices that may use a magnetic field to control an electric current. The effect of spin transistors may be similar to the effect of conventional transistors. An electron may have two spin states: spin up and spin down. The spin states of the electron may be control parameters in conventional transistors.
Conventional spin transistors may have an additional control parameter, namely, a magnetic field. The magnetic field used by a conventional spin transistor may control the electric current by manipulating the spin states of electrons. Thus, electronic devices including conventional spin transistors may have enhanced functionality as compared to electronic devices including only conventional transistors.
Conventional spin transistors may include a bi-potential energy barrier structure (i.e. two potential energy barriers may be combined with a magneto-resistant device in the conventional spin transistor). The bi-potential energy barrier structures may be configured to allow magneto-electric current to pass through the conventional spin transistor.
Other conventional spin transistors may include a first and second n-type ion-doped silicon substrates placed such that each substrate is oriented toward the other. The first and second n-type ion-doped silicon substrates may be vacuum adhered to form an emitter and a collector, respectively. A metallic spin valve (i.e., a base) may be placed between the first and second n-type ion-doped silicon substrates.
The conventional spin transistor may further include two pairs of layers. The first pair of layers may include an emitter (i.e. the first n-type ion-doped silicon substrate) and a base (i.e. the metallic spin valve), the pair of layers formed of platinum (Pt) and Cobalt (Co), respectively. The second pair of layers may include a base to collector (i.e. the second n-type ion-doped silicon substrate), the pair of layers formed of Copper (Cu) and Co, respectively. The above-described first and second pair of layers may form a Schottky barrier diode structure.
When a forward voltage bias is applied to the emitter (i.e. the first n-type ion-doped silicon substrate) and the base (i.e. the metallic spin valve), the hot electrons may exceed a threshold of the energy barrier and may flow through the energy barrier and into the collector. The conduction of the hot electrons may depend on whether the magnetizations of the two Co layers (i.e., the two potential barriers) included in the metallic spin valve have a same direction.
If the external magnetic field is small, the states of the two Co layers may be anti-parallel. In this case, the spin up or spin down electrons may be spin inelastic scattering and the current flow of collector may be relatively small.
If the external magnetic field is large enough to align the magnetizations of the two Co layers in parallel, the probability of spin up electrons flow may increase, thereby increasing the electric current. With conventional spin transistors, a current fluctuation rate of more than 200% of the magneto-electric current may be obtained at ambient temperature. However, the electric current output of conventional spin transistors may be small, thereby limiting their utilization in lower current applications, (e.g., in a range from 1.287 pA to 44 pA). Further, conventional spin transistors may be more difficult to miniaturize.
Another conventional spin transistor may include a magnetic tunnel layer formed as a base adjacent to a collector, the collector being formed by an n-type GaAs substrate. The conventional spin transistor may be a Schottky barrier diode structure. An aluminum layer may be formed on the base and may be oxidized into an aluminum oxide (Al2O3) layer. An emitter layer may be formed on the aluminum oxide layer, thereby forming another Schottky barrier diode structure. The above-described structure may reduce existing problems in the manufacture of conventional spin transistors, including miniaturization and/or an increased magneto-electric current fluctuation rate. For example, by this method, a current fluctuation rate of more than 3,400% at lower temperature (e.g., 77 Kelvin) may be achieved. However, the GaAs substrate may have a higher cost and/or the aluminum oxide layer may not be formed as a uniform layer. Further, the above-described conventional spin transistor may require a lower electric current input so as to reduce or prevent damage to the aluminum oxide included in the aluminum oxide layer. Accordingly, since only lower electric current input may be used with the above-described conventional spin transistor, the electric current output of the conventional spin transistor may also be lower, thereby limiting their use to lower current applications. Further, the above-described conventional spin transistor may have the additional requirement of operating only at lower temperatures in order to provide an acceptable magneto-electric current fluctuation rate.
Yet another conventional spin transistor may include a magnetic tunnel transistor, which may increase the operating temperature of the bi-potential energy barrier spin transistor. At ambient temperature, the conventional spin transistor may provide up to 1 μA of electric current output and/or the magneto-electric current fluctuation rate may increase up to 64%. In this conventional spin transistor, a cobalt-iron alloy (Co84Fe16) layer of 3 nm may be formed as the base on an emitter formed of a n-type GaAs substrate. An aluminum layer oxidized into an aluminum oxide layer may be formed on the cobalt-iron alloy layer (i.e. the base). A (Co84Fe16) layer of 5 nm may be formed as the emitter on the aluminum oxide layer. A pinning layer may be coated on the emitter. The pinning layer may include anti-ferromagnetic Ir22Mn78. The pinning layer may be capable of pinning the magnetic dipole of the emitter. The pinning layer may be covered with a tantalum (Ta) layer of 5 nm. The magnetic dipole of the base may be modified without affecting the magnetic dipole of the emitter. Thus, the spin direction of the injection electron may be controlled.
However, the above-described conventional spin transistor may include a GaAs substrate. The GaAs substrate may be expensive. Further, the aluminum oxide layer may not be formed as a uniform layer. Since the magneto-resistant device with a higher current fluctuation rate may require a higher-quality (i.e. uniform) layer, the complexity of the manufacturing process may increase as a more uniform aluminum oxide layer may be difficult to produce.